Can anyone give me a quick tip on where the oxygen sensor connector is located in the engine bay on an S4 Spider? I'm trying to troubleshoot a pesky check engine light.

Also, the Cardisc CD doesn't seem to have the Bosch wiring diagrams? They're listed in the table of contents for the chapter on the electrical system, but the pages aren't there. Anyone else notice this? If I could find them I'd at least know what color wires I'm looking for...

I think its a two wire. One heater, one reading. Right in that same vicinity there are a couple more wires. Don't know what they are for, but best guess is reverse lights. I will snap a picture of the two you are looking for and post up in a little while.

Eric, you are right, its a three wire. Gubi, it has two connectors under the hood. The box connector has two white wires coming out and I believe that is the heater. The round orange cap connector is the computer feed. You can take your measurements from that connector with the red lead on a digital multimeter.

You can see these two connectors on cardisc under Service Manual - Fuel System on page 21.

Here is a picture of the two connectors you are looking for. Be sure to keep these wires off the manifold if you have to reinstall a new one.

Hmmm...well I tested it last night and it's bouncing between 0.2 and 0.8 volts, which from reading the service manual is pretty much what it's supposed to be doing. However, I couldn't get the light to come on while I was testing it, so it's possible I have an intermittent bad connection somewhere. It's also possible it's clogged injectors, a failing air mass flowmeter, or an air leak somewhere that I can't find.

I'm taking it in to my mechanic on Saturday so we can slap it on the emissions meter and figure out exactly what's going on...at this point I'm not sure if it's lean or rich. Hopefully some additional testing will shed light on the issue.

No, it didn't stabilize. When I first started it (engine was semi-warm) it was hovering around a stable 0.47, but then as it warmed up it started moving up and down between about 0.2 and 0.8. Only ran it about 10min, though. The service manual said something like "should move between 0 and 1 volts" or something like that, so I'm assuming this is normal behavior. Should it be doing something else?

That sounds good that it started off where it belongs. Sounds like you got something other than the O2 sensor. I would check all those hoses very carefully. Across the top of the motor and the intake rubber runners as well.

I dunno, man, those hoses look pretty good. I even pulled off the hose to the carbon cannister just to see what it would do with a big intentional leak - didn't make a lick of difference.

My money right now is on an intermittent bad connection to the O2 sensor. Failing that, I'm going to look at the AFM calibration and double-check the fuel pressure. Could also just be clogged injectors, I suppose, but the engine power seems fine.

Yeah, the sensor's pretty new - I just had it installed in October. Old one had 85k on it, so I figured it was definitely time.

I don't have my Cardisc here, but if I recall correctly the 1223 code means "lambda sensor at control limit" or something like that. The 1224, which I only saw once, is that the lambda sensor voltage is out of range.

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